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The point made concerning engine complexity and the implications for subsequent owners is well made.
Much as I am an an advocate of turbocharging to increase (diesel) engine efficiency, my feelings are that the widespread adoption of this to petrol engines will render them "not worth having" at over 5 years old.
Unlike a diesel, the exhaust gas temperatures are sufficiently high on a petrol engine to shorten the life of a turbocharger even when correctly used. Neglected oil changes, the wrong oil and a lack of cool down (motorway stop) will cause early death.
Keep the job simple to ensure that the total cost of ownership is minimised, together with "production pollution". An early death of an elaborate machine only benefits its maker.
659.
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The cooldown isn't really necessary with watercooled turbos-and if the manufacturer is really worried about it they can (and sometimes do) use a second electric water pump.
Average EGTs of a petrol are only in the 450-600 Celcius range-roughly what a heavy duty diesel copes with all day long-and their turbos last fine.
Of course no engine (petrol or diesel) can sustain 75+hp/litre for very long, but most cars will never be required to do so for more than a few seconds at a time. There's no point building passenger car engines to hd standards. Most cars get scrapped with very little wear to the engine and what wear there is is usually attributable to bad maintainance. There's the top percentile of drivers who push their engines too hard-but that's their problem.
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VAG forums are littered with problem posts about their TSi range, I wonder if it's just internet magnification of a small minority, or if there is a significant problem. Their track record for reliability is pretty mediocre in the last few years and Audi/Vw regularly lie towards the bottom of reliability surveys, especially in the US. My BIL has just got rid of a Touran which was a nightmare car, VAG relieved him of £1000 and then told him he needed a new turbo as well for £1200!!! I've been lucky with my Octavia but even that needed a new turbo (£1000) after 15000 miles!
Much as I like the idea of the 1.4 tsi, especially in an Octavia, I think I may avoid until longevity and durability are more proven.I'll probably opt Japanese instead and go for non turbo petrol, simple as possible.
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I'm a member of Toyota Yaris and Audi A2 forums.
The Tota Yaris outsold the A2 in the UK by about 10:1.
On the forums, A2 technical problems outnumber the Yaris technical problems by about 20:1.
Says it all.
Edited by madf on 20/08/2011 at 16:30
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I drove a 1.4 turbo a while back, it was an Alfa Mito, not a VW. Initially I was a bit skeptical, and thought it would be laggy. I was wrong though, there was almost no lag and it didn't need working hard at all.
In contrast, I drove a Fiat 500 TwinAir a while back and that was very poor. It was laggy and needed to be abused to get anything out of it.
I think they are probably a good idea, but I also love the simplicity and low maintenance costs of my current engine, which has a chain cam.
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low maintenance costs of my current engine, which has a chain cam.
Until the tensioner goes...or the oil pump drive...or the chain simply stretches through old age. Chains work well on pushrod engines but the correct way to drive an OHC is via a toothed belt. The simplicity of the belt outweighs the cost of changing it. With 70,000 mile intervals there's a good chance that an engine will require the same number of replacement belts as chains over the course of the life of the engine-one.
The quicker the chain fad dies the better.
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Chains usually give you plenty of (audible) warning before they go - belts just snap or slip due to waterpump failure or missing teeth. I cannot remember many instances of engines wrecked from snapped cam-chains in the "old" days - they'd make a nasty noise 'til you changed 'em - the same cannot be said for belts. Yes I know the current BMW/PSA engine has an issue with cam-chain tensioner failure. That's one model in a sea of cars with cambelt issues.
I'm glad this fad for belts is dying.
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I cannot remember many instances of engines wrecked from snapped cam-chains in the "old" days
That's probably because they were pushrod engines which use very short chains. With a bit of luck, the trend for turbocharging will convince OEMs to put the cam (singular) back where it belongs-in the block. The amount of effort that goes into making an engine 6000+RPM capable is incredible-and almost completely wasted.
Mounting the cam low in the block makes the chain/belt argument moot since gear drive is a viable option. Let the turbo do the breathing.
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That's probably because they were pushrod engines which use very short chains. With a bit of luck, the trend for turbocharging will convince OEMs to put the cam (singular) back where it belongs-in the block. The amount of effort that goes into making an engine 6000+RPM capable is incredible-and almost completely wasted.
Mounting the cam low in the block makes the chain/belt argument moot since gear drive is a viable option. Let the turbo do the breathing.
I never knew that was why OHC became standard. Now you've explained it makes sense - and seem as useless as you say. I generally repeated the mantra of OHV:old, clunky, OHC: modern, whizzy without giving it much thought.
Silly really as most small capacity OHV I've driven are grunty enough...
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The quicker the chain fad dies the better.
Normally I would agree with you unthrottled but that's nonsense. My BMW's chain driven engine was smooth and quiet and showed no signs of breaking when I sold it at 160k.
Likewise a mates Nissa Micra has 165k and there is no noise from the chain - of course it gets regular oil changes as mine did.
There were problems a few years ago with certain engines - VR6's, Vauxhall 24v's, the old Jag XK's, but chain design is better these days.
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So has belt design. Belts got a bad rep because people (understandably) did not like having to pay to have the belt changed every 40,000 miles. Nowadays the timing belt change interval is usually 70-100,000 miles.
A bad timing chain can write off an old car because it is expensive to change so if the chain gets noisy, they'll leave it until it goes.
A belt has a simple tensioner and does not rely on lubrication. The same is not true for chains.
I don't doubt your good experiences with chains. However there are enough people who have suffered the expense of a failing chain to question the fabled infallibility of chains.
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Belts age, chains don't, belts being external can become contaminated with oil or coolant which will shorten their life. VAG engines had problems with tensioners failing well before the service interval, as do volvo XC90s and Vauxhall 1.7 diesels, there aren't many manufacturers that haven't had cambelt or tensioner issues over the years..These are failures 2 or 3 generations into general cambelt usage, so they're not teething issues. A camchain may well last forever (out-live the rest of the car) you cannot say the same for a belt which is quite likely to snap if abused. I suspect the move back to chains is to reduce service costs to make the car more appealing to fleet buyers.
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I don't see how coolant could get under the timing cover. An oil leak? possibly, but engnes shouldn't be leaking oil! The belt is fairly well protected under its cover-and much cheaper to change when it does require replacement.
The use of cheap tensioners is a fault of penny pinching-not an inherent design flaw of belts per se. There have been plenty of problems with hydraulic chain tensioners-
A camchain may well last forever (out-live the rest of the car) you cannot say the same for a belt which is quite likely to snap if abused.
Try a bump start with a hydraulic tensioner! Let the clutch out too quickly and the chain will slip. I've replaced belts at 60,000 miles and there's never been any sign of wear. Who knows how long it could have soldiered on for? But , like you say, there's little/no warning of impending belt failure so you don't riskit.
I agree that not having a scheduled change is an incentive for fleet users. However,the move to chains seems to have stalled, if not actually receding.
Give us our OHV engines back and let's consign these metallic and rubber anacondas to the bin!
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OHV's belong in a dustbin. Along with those horrible rattly things Ford used to use.
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Why?
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Because.
That good enough? :)
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I've got a big 3.0 V6, OHV, in my fun car, it's a dream to work on, everything easily accessible, it don't rattle, it's got a fan belt that works the water pump, and timing gears!! I wouldn't change it for anything.
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Is that the Ford Essex V6. The cam timing gear is not made of metal and can fail in the same way a cam belt does. Fortunately you usually get a "knock" before it does. Also beware the haxagon oil pump drive shaft fed from the distributor going round (no oil pressure). Other than that - great engine.
Sorry showing my age!! Used to drive/maintain mk IV zodiac & zephyrs
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The cam belt is frequently used used to drive the water pump of modern cars, the additional load on the bearings to withstand the tension required of a cambelt means failure is common - as is the seal failing weeping coolant.
The vast majority of hydraulic tensioners have a ratcheting non-return system so bump-starting issues are irrelevant.
Given the low-rev ceilings of diesel engines OHV would make a lot of sense.
Edited by SteveLee on 21/08/2011 at 01:19
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I stil don't get the advantage of driving the water pump with the cam belt. I was more concerned about freezing than leaking. My coolant turned to mush last winter and I was glad ithe pump was run off the ancillary belt.
I didn't know about the ratcheted tensioners-this makes sense. I was told to be very careful about bumping a chain engine because of the potential slipping problem.
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Give us our OHV engines back and let's consign these metallic and rubber anacondas to the bin!
But isn't the point of DOHC 4/5 valves per cylinder is that you can get better efficiency by allowing more air flow into the engine? I'm not particularly a fan of this set up - I would like a lower revving turbocharged torque monster of a petrol engine, but bringing back pushrods just wouldn't allow the manufacturers to meet emission standards.
They had a few problems with the OHV short chain set ups of course - the fibre teeth shearing on the gears of the Ford V6 Cologne engine. I can't remember if the Essex V6 suffered from this. It's always said that one of the reasons they changed to belts was to reduce engine noise - I can't say that my BMW straight six was noisy - yes, there was a slight metallic zing if you were standing outside at the front of the car, but I could still hear the injectors quietly ticking away. Maybe this set up was properly designed though. I think the noise issue was over played.
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'Emissions' are invariably blamed for the discontinuation of any engine! Regardless of valvetrain arrangement, 2 valvers tend to be better emissions wise than 4 valver. The EGTs are a bit higher and this helps the cat-especially on turbo engines. The higher intake velocity at low RPM should give a slightly faster burn.
Breathing efficiency is a double edged sword-it kills intake velocity at low load/RPM-which is where the engine tends to spend most of its time. I think the answer is to turbo a mechanically robust and simple engine. When you can change the density of the intake charge, volumetric efficiency is irrelevant. Smallish cylinders, fixed valve timing, no balance shafts etc. Flat torque curve over 1500-4500 RPM.The OHV keeps engine height down as well. Good for low bonnet profiles and pedestrian safety requirements.
The high winding fours are not really very well thought out. I can't imagine a Honda Accord or Toyota Avensis driver revving their engines to the 6000+RPM required to make maximum horsepower, but you still have to engineer the engine to do so because that is the rated RPM. This is wasted effort.
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The high winding fours are not really very well thought out. I can't imagine a Honda Accord or Toyota Avensis driver revving their engines to the 6000+RPM required to make maximum horsepower, but you still have to engineer the engine to do so because that is the rated RPM. This is wasted effort.
I have revved my Avensis engine to those speeds and it's not an unpleasant sound, but it 's reluctant to do it, you can tell the fuelling is set up for economy. Funnily enough, for a sixteen valve engine it produces it's best work at low revs and the mid range, so I can see your point about questioning a DOHC's multi valves purpose these days.
Edited by corax on 21/08/2011 at 15:25
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There's always one! :)
The problem with revving is that is is so inefficient. If it takes, say, 10hp to spin a 2 litre 4 pot at 3000 RPM, you need about 30hp to spin the engine at 6000 RPM. (And I didn't include balance shafts in this calculation...)
The noise an engine makes at high speed isn't a result of power, it's a result of friction.
When everyone is trying to get as much useful work from as litte fuel as possible these days, the screaming DOHCs look far more obsolete than their OHV ancestors!
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How can an engine tell a bump start from a starter start-they both turn the flywheel?
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you'll get much higher cranking speed with a bump start. The more salient issue is the inexplicable urge to dump the clutch which shock loads the crank and associated pullies in a way that the starter motor won't.
I bump my car in traffic jams and haven't had any problems. Good ol' belts. ;)
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Theres a bucket load of old b******s spouted by our self professed experts in this thread....
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Theres a bucket load of old b******s spouted by our self professed experts in this thread....
Well thanks for redressing the balance :)
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Four valves per cyclinder are advantageous in mildly tuned engines for a number of reasons, you can achieve good flow with minimum valve lift, that combined with smaller individual valves means you can use softer springs. The softer cam timing to achieve the same flow means the valves spend more time on their seats aiding heat dissipation reducing the risk of pre-ignition, the valve seats, valves and valve retainers get a much easier time from the lighter springs – noise will be reduced too. You can run higher compression ratio thanks to the reduced exhaust valve temp, reduced valve lift will assist your design aims for a compact combustion chamber with smaller and shallower pockets on the pistons – if they are needed at all. You could also pop one inlet value open ahead of the other increasing initial inlet charge speed, improving swirl at low revs although this is rare because the improvement is marginal against the cost of having to grind camshafts on another plane. 2 valves per cylinder are rare today for very good reason – 4VPC are not all about making horsepower way up the rev-range.
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Your comparison is accurate-providiing we stick to naturally aspirated engines. There is no reason to.
You can use a short duration, short lift two valve set up allied to a turbocharger which will solve the high RPM breathing problem. When turbochargers are involved, the breathing of the head is almost totally irrelevant. Take VWs ubiquitous 2V 1.9 PD engine. Not only is it a 2V-but it is contraflow-ugh! Doesn't matter a jot. The 4V that replaced it was still a contraflow and the engine isn't any more efficient than the 2V- although it is cleaner.
Opening one intake valve slightly before the other does not not yield meaningful swirl. The only way to get swirl of non negligible magnitude (that does not decay during the rest of the intake and compression stroke) is to effectively shut one valve and emulate er...a 2 valve set up.
Without variable intake geometry, intake charge velocities are too low under throttled conditions (most of the time) with 2 intake valves.
The cool running exhaust port/valve is a boon as far as running hard is concerned. But the extra valve seat area is a headache for achieving catalyst light off temperatures. This is especially true when there is a turbo in the way.
The single large exhaust valve can be cooled reasonably well with hollow stems-paid for scrapping a cam and 2 valves per cylinder.
The is simply no evidence that 4 valve PR heads have more efficient combustion than wedge heads. Combustion duration and heat transfer are very similar for both.
As far as SI engines are concerned, the 4V was born out of the 'necessity' of staying naturally aspirated. Turbos render them redundant.
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By talking about increasing CR, keeping exhaust valves cool and avoiding detonation I'm clearly talking about petrol engines. Of course how a head breathes doesn't matter much with turbo-charged cars.
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Air flow is important in diesels too.
However sticking with SI engines, my argument in favour of 2V OHV is in conjunction with turbo charging. The simplification of the valvetrain and inlet manifold would represent a useful saving that could go towards a turbo.
I still think that it is interesting that GM scrapped the Northstar and kept the Gen III OHV engine. In fact the LS series has seen off quite a few of its pentroof DOHC competitors. You can't tar all OHV 2V engines with the same brush as the Buick 215 junk.
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A good example of modern 2V engine would be the 1.4 TSI's little brother-the 1.2TSI. It's underesquare, has a high static compression, and has the same specific output as the 4V 1.4.
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The Buick 215 was so rubbish it won the 1966 F1 champioship in standard (Rover) form and GM begged Rover for the design rights back (after Rover had ironed out all the design issues with the original) it then went on for another 30+ years in various guises - not bad for a piece of junk. I've had a few turbocharged Rovers V8s (shoe-horned into various cars) over the years, I'm surprised Rover didn't follow that path as they were particularly suited to turbocharging, light, reliable 400 bhp as easy as falling off a log.
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Turbocharging would have required effort-which was an anathema to Rover and British Leyland. They had a half-a***d collaboration with Perkins to try and produce a diesel-which predictably failed. Oh well, they got a forged crank out of the project.
About all they did was to keep boring and stroking until they ran out of metal.
GM did ask for the tooling back. But once Rover refused, GM went back to the drawing board and designed the 3800 V6. This was a more sensible configuration for a 3.5 litre engine since 8 cylinders is not warranted in this displacement. This went on to become a classic. GM did turbo and supercharge the engine and a modifed version is still in production. Where's the 215?
GM worked much harder with their V8. They got the fluid dynamics of the head sorted-the Vortec head has a brilliant combustion chamber. They got rid of the siamesed ports. They tightened the production tolerences so the engines can go huge mileages without needing to be rebuilt. How many 215s can go past 100,000 miles without major work?
They sorted out variable valve timing and cylinder deactvation to improve the fuel economy and emissions. That's why GM's pushrod engine is still in production and Rover isn't.
Quarrelling aside, the turbo 215 sounds good. Are you running single or twins? Draw through, blow through or EFI?
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About all they did was to keep boring and stroking until they ran out of metal.
What a great line. I'm glad you're only talking about engines :)
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Rover stopped developing the “buick” V8 decades ago, it was generally used in off-roaders (which hadn't yet become wagmobiles) torque and driveability was deemed more important which the Rover V8 excelled at, it was left alone because for the target market they didn't need to touch it, there were more pressing problems given very limited budgets, there was a previous DOHC 4VPC project that got shelved to save money (as usual) with two cylinders knocked off this engine is what powered the Metro 6R4. The GM engines of the late 80s (when Rover stopped developing the 215) didn't have all the fancy stuff either – let's compare apples with apples! GM took over a decade and many millions to develop the Northstar. Jaguar knocked it into a cocked-hat in 6 months flat on a shoe-string with the AJ-V8, lighter more powerful and more efficient. The Brit engineers can do it if they get the cash. The Rover K-series is an incredibly thermally efficient engine – why do you think it's STILL around? The engineers get something new on the bench and it isn't as good, so they continue to develop the K – as the Chinese have - rather than start from scratch on a “worse” engine. The (stepless) variable valve timing system on the VVTS K-series was much more sophisticated than the two stage Honda systems of the time, in gear roll-on wise a 1.8 VVC Rover 25 Gti bettered the “mighty” Golf VR6 of the day – not bad for a company with no money.
I've seen plenty of Rover V8s with 200+K miles on them - they only die if oil changes are neglected (sludge problems like GM 4 pots turbos), auctions were at one time full of police Rangies with 160-180K on the clock. Later engines suffered from porous blocks as, yes, the capacity was stretched too far combined with old tooling – what do you expect from a company that struggled along for years without cash? Talking of which, GM went bankrupt in 2009 – the US government bailed them out – that's why they are still here unlike Rover and it's not the first time GM have been near the edge.
Rover couldn't do turbos? Have you ever driven a 620tti or a Maestro Turbo?
The Vitesse Turbo was an intercooled twin (T3) turbo set-up blowing through the stock Efi. It made 400bhp easily at fairly low boost levels. Another 3500S I had was a blow through (Metro Turbo T2+sealed SU per bank) lash up - it still made 350bhp – you could still pull away in 5th gear! Both engines lasted over 80K in supercharged form before the cars were sold-on. Before it was modified, the Vitesse was quicker than my friends (standard) Sierra Cossie which (on paper) was much quicker. Although lacking peak power the Rover had power everywhere, didn't really matter what gear you was in- it just ripped - much faster than the 190bhp figure suggests. The Cossie had to be wound up to extract performance from it.
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The Maestro turbo and even the A series 1275 turbo were amazing-I'll give you that. Power band as long as the wall of China, not some peaky dyno queen.
I suppose my derision of the Rover 3.5 comes from the fact that it could have been so much better. Why take the bore to 3.7" and end up with thin cylinder walls when you've got a stubby 2.8" crank?? Australia had the right idea. Put a 3.5" crank in and end up with 4.4 litres.
There's no point building an oversquare engine for low end torque. A 2.8" crank should be screaming. But the valvetrain wasn't good enough for revving. The lifter bores weren't rigid enough. They ended up bodging the lifter bore problem and borrowing Volvo parts to build high output racing engines! And why did it take it take them so long to dump the 4 problematic head bolts?
The K series? On the whole, a good engine-as you say-very efficient and capable of a lot of power. But the fact remains that other companies got wet liner engines to work and Rover ended up with a foreseeable head/gasket problem that should have been ironed out in development. British Leyland were too big to play the cash-starved underdog card. They had economies of scale that should have allowed them to compete.
Jaguar knocked it into a cocked-hat in 6 months flat on a shoe-string with the AJ-V8, lighter more powerful and more efficient
Sorry Steve-you're not getting away with that! Ford had a lot of input into that engine. Jaguar never wanted to build a V8-although had they built a V8 instead of the V12 white elephant, they might have maintained their independence. When Ford took over Jaguar, they were horrified at just how bad Jaguar's problems were. They pumped a lot of money into Jaguar. Most car companies are cash strapped, but it only seems to be the British ones that play the poverty card. Anyone can have innovative ideas. The skill is getting the execution right.
Edited by unthrottled on 24/08/2011 at 02:08
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Ford had practically zero input into the Jag V8, after its success they may pretend they had a hand – they didn’t – I worked for Ford at the time. Jaguar were playing with the idea of a V8 for years they were not against the idea, just against the idea of being forced to use a Rover V8 which is why they made the XJ40 engine bay so narrow. Ford were working on a Northstar beater for years, a huge project that cost 10s of millions, when Ford took over Jaguar they gave them the money to develop a variable valve timing system for the forthcoming Ford V8. With the money and without Ford's knowledge they designed and built the AJ-V8 in six months flat. Ford were incensed when they found out, Ford took the engine back to Dearborn to test it, it slaughtered the in house Ford project, lighter, more efficient and more powerful, to rub salt into the wounds and despite having a much higher rev ceiling, it double the MTBF test of the Ford unit too. Stunned Ford then commissioned Jaguar to design a low-tech version for the Lincoln. Ford helped “productionise” the project but that's all they did. The AJ-V8 at launch was the best V8 in the world. I was in the meeting where Alex Trotman (then CEO) said they (Ford) thought they could teach Jaguar a thing or too about engineering – it turned out very much the other way round. I read an article somewhere describing the (co design of the AJ-V8 and the importance of Ford's input - it is complete fantasy by embarrassed Ford engineers.
Yes Ford helped immeasurably with quality control, but as engineers, Ford could not touch the boys from Brown's lane.
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Well that is an eye opener, Steve.
I knew that they designed the engine bay of the XJ40 to be too narrow to fit a V8 without redesign so I assumed that they didn't want a V8.
I guess they learned a great deal from the V12 debacle.
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Jaguar had a V8 based on a chopped down V12 lump running on the bench 30+ years ago, by some co-incidence it shared the Rover V8's 3.5 litres and easily topped 200bhp, sadly the BLMC management pointed at the Rover V8 as an alternative Jag engineers simply would not even consider putting an OHV engine under their bonnets - hence the narrow XJ40 engine bay - which you could (just) fit the V12 into (and therefore the potential Jag V8). The Rover was much wider being 90 degree. The Jag V8 was 60 degree being a cut down V12, obviously balance shafts and crank counter-weighting technology weren't what it is now, as such, the Jag 3.5 V8 was quite a vibey beast by all accounts.
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Is a 60 degree SOHC engine narrower than an OHV 90 degree engine (for a given stroke)?
A 60 degree V8 sounds a bit daft. Split crankpins, balance shaft(s?), flying arms and all the rest of it.
After all, Jaguar weren't too proud to reach for an old heaton blower to spice up their engines. I wonder just how much damage the internal politics did to the companies under BLMC. Probably quite a lot!
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I suspect the Jag engineers were well aware that they were making a pig's ear out of a silk purse with a 60 degree V8 - that's budget contraints for you. Renault made the same mistake with thier 72 degree V6 (PRV) - the dregs of an abandoned V8 project turned into a rather average lash-up of a V6.
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So they couldn't decide on a 60 degree V6 or 90 degree V8 and decided to split the difference in the valley angle-how very Renault! Surprised they didn't compromise on seven cylinders while they at it!
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>> Rover couldn't do turbo's? Have you ever driven a 620tti or a Maestro Turbo?
I owned a Montego Turbo in black, raised boost, and it was the most fun car I've ever had. A bit of lag, but once that Garret T3 turbo kicked in, wow. Mine was a later model - torque steer virtually banished by lowering the engine slightly. Very strong engine, good handling - I drove to Loch Leven in Scotland on holiday - what an epic drive that was, hills didn't exist in that car. It was even good on the snow covered roads coming back - a bit drifty but stable and predictable. I was lucky though, because a few weeks after I got back it started stuttering up the road - that's when I found it had no fuel filter and the SU carb was full of muck. I fitted an in line filter.
I just wish it had had Bosch electrics - the Lucas ignition units were useless, I got through three, and mine were the later rarer ones.
The other thing I'll say about that generation of Rover is that the cabin space and comfort was very good. I also had a Rover SD1 V8 and this could have been a brilliant car if the damn things had been put together properly.
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